Cotter Pins

Split pins are frequently used to secure other fasteners, e.g. clevis pins,

as well as being used in combination with  hardboard discs as a traditional

joining technique for teddy bears.[6] A common application of this is when

used to secure a castellated nut. One problem with this type of use is that

the castles on the nut must line up with the hole in the mating part so

that the split pin can be installed. When the nut is torqued properly, but

the holes still do not line up, it is preferable to overtighten the nut than

undertighten it.